1) Technical Field of the Invention
The present invention relates to a power semiconductor device used for controlling large current of an electronic equipment such as a motor and heater. In particular, it relates to the semiconductor device capable of predicting the timing when a metal wire is likely to fail (disconnect).
2) Description of Related Arts
In general, the power semiconductor device (referred to as a “power module” herein) is used as a power source for supplying a substantial amount of current to an electronic equipment such as a motor and heater. Thus, if the power module fails to supply a desired controlled current, the electronic equipment incorporating the power module cannot achieve predetermined functions, and even worse, may often have a fatal problem such as a burnout due to an overcurrent. Therefore, such a power module is required to have a fairly high level of reliability.
Meantime, so-called an Intelligent Power Module (IPM) has already been commercialized, which includes a self-protecting circuit for safely suspending its function to supply a power for others when the power module fails, so that the electronic equipment using the power module can be protected from any devastating damages by continuously receiving an excess of or uncontrolled current.
For example, JPA 8-195411 discloses a plurality of strip fuses provided between a terminal and a switching element such as an Insulated Gate Bipolar Transistor (IGBT) chip. When the overcurrent is flown through the switching element, the strip fuse blows preventing smoke and burst (fatal damage) of the IGBT chip. Also, it discloses a chamber encompassing the strip fuses that is filled with arc-extinguishing material.
However, the power module disclosed in the prior art reference is to avoid the fatal problem due to the overcurrent flown through the power switching element to the power module and the electronic equipment incorporating thereof. Therefore, once the power module is damaged by the overcurrent and safely suspends the function of the electronic equipment, the damaged power module has to be replaced so as to again supply normal or controlled current to the electronic equipment. Thus, it is essential to replace the damaged power module with a new one, however, it cannot always be expected that the new power module for replacement is kept in situ, which eventually brings users excessive disadvantage and inconvenience.
Even with the highest level of technique used for manufacturing the power module, it is quite difficult to produce the power module eliminating the possibility of failure due to thermal stress by Joule heat generated from itself and mechanical stress by oscillation transmitted from the electronic equipment, as the power module is being used. In fact, it is almost impossible to manufacture the perfect power module free from any failure eternally.
To avoid the fatal damage of the power module, a regular maintenance is conducted for maintaining the electronic equipment always in a good condition, in which any components possibly causing the fatal problems are routinely inspected and replaced with the new one. Thus, the components that may cause big problems are often replaced before the timing when they actually fail.
Nevertheless, since operation conditions in use substantially give influence to the timing of possible failure when the power module is likely to fail, the timing of possible failure is often inconsistent with the timing of actual replacement. Thus, in some cases, the power module fails before the regular maintenance, or in other cases, it is uniformly replaced with the new one even though it could still be used much longer. Therefore, the same disadvantage suffered in the circumstance where no maintenance is conducted cannot be eliminated, or the maintenance cost is raised because of the undue replacement.